1. Field of the Invention
This invention relates to a connector, and more particularly to a connector for differential signal transmission.
2. Description of the Related Art
Conventionally, there has been proposed a connector for high-speed differential signal transmission, comprised of signal contacts, ground contacts, and a housing which holds the contacts (see Japanese Patent No. 3564555).
The signal contacts include plus signal contacts and minus signal contacts, each plus signal contact and each minus signal contact forming a pair. The plus signal contact and the minus signal contact, forming each pair, are disposed at adjacent to each other.
The plus signal contact, the minus signal contact, and the ground contact each include a terminal portion which is inserted through an associated one of through holes of a printed circuit board.
The terminal portions of the plus signal contacts, the minus signal contacts, and the ground contacts are arranged in three rows. The terminal portions of pairs of plus signal contacts and minus signal contacts are arranged in an upper row, the terminal portions of the ground contacts are arranged in a middle row, and the terminal portions of pairs of plus signal contacts and minus signal contacts are arranged in a lower row. The terminal portions of the plus signal contacts and the minus signal contacts in the upper and lower rows are arranged at substantially the same pitch. The terminal portions of the ground contacts in the middle row are arranged in a manner displaced by half pitch from the terminal portions of the plus signal contacts and the minus signal contacts in the upper and lower rows.
If the terminal portions of a pair of a plus signal contact and a minus signal contact in the upper row and the terminal portion of a ground contact in the middle row, adjacent to those contacts, are connected by virtual lines, an isosceles triangle with the terminal portion of the ground contact at the apex thereof is formed. Similarly, if the terminal portions of a pair of a plus signal contact and a minus signal contact in the lower row and the terminal portion of a ground contact in the middle row, adjacent to those contacts, are connected by virtual lines, an isosceles triangle with the terminal portion of the ground contact at the apex thereof is formed. One isosceles triangle of the above-mentioned two isosceles triangles is an inverted triangle having the top positioned below, and the other is a triangle having the apex positioned above. These triangles are arranged in an alternating manner in a horizontal direction in a state slightly displaced in a vertical direction.
The printed circuit board on which the above-mentioned connector for high-speed differential signal transmission is mounted is formed with the through holes in a layout associated with the above-mentioned layout of the terminal portions of the plus signal contacts, the minus signal contacts, and the ground contacts, and is formed with plus signal lines and minus signal lines, which extend to the through holes associated with the terminal portions of the plus signal contacts and the minus signal contacts.
Each pair of the plus signal line and the minus signal line on the printed circuit board, extend to the respective associated through holes, in parallel to each other, maintaining a certain distance therebetween.
However, as shown in FIG. 9, the distance between the plus and minus signal lines SL′ and SL′ which extend to the associated two through holes 21a and 21a which are associated with the terminal portions 51d′ and 52d′ of the plus and minus signal contacts forming a pair in the upper row is slightly increased immediately before the plus and minus signal lines SL′ and SL′ reach the through holes 21a and 21a. 
Further, the distance between the plus and minus signal lines SL′ and SL′ which extend to the associated through holes 21a and 21a which are associated with the terminal portions 51d and 52d of the plus and minus signal contacts forming a pair in the lower row is largely increased immediately before the plus and minus signal lines SL′ and SL′ reach the through holes 21a and 21a. This is because it is required to space the plus and minus signal lines SL′ and SL′ which extend to the two through holes 21a and 21a associated with the terminal portions 51d and 52d of the plus and minus signal contacts forming the pair in the lower row from each other so as to prevent the plus and minus signal lines SL′ and SL′ from interfering with a through hole 21b associated with a terminal portion 61d of a ground contact in the middle row.
As described above, the distance between the plus and minus signal lines SL′ and SL′ on the printed circuit board 21′ is partially increased, whereby a range in which the plus and minus signal lines SL′ and SL′ are not parallel to each other is increased, which makes crosstalk liable to occur between a pair of signal lines SL′ and SL′, and the adjacent other pair of signal lines SL′ and SL′, and also makes it difficult to carry out impedance matching.